In order to stabilize electric discharge irrespective of an electric resistance fluctuation, of a charging roller (charger) as a charging member, due to a change in environment in which the image forming apparatus is provided and in environment of an inside of the image forming apparatus or irrespective of an electric resistance fluctuation of the charging member due to deposition of a toner and an external additive on the charging member with an increase in number of sheets of image formation, discharge current control, in an image formation preparatory rotation period from input of a print signal until an image forming step operation is actually made, in which a value of an AC current flowing when AC voltages having peak-to-peak voltages of 6 kinds are applied to the charger is measured and the peak-to-peak voltage of the AC voltage to be applied during image formation is determined on the basis of the measured AC current value is described in Japanese Laid-Open Patent Application (JP-A) 2001-201920.
As described above, it is expected that the electric resistance fluctuation of the charging member is generated, and therefore the discharge current control may preferably be carried out, in addition to the image formation preparatory rotation period described in JP-A 2001-201920, during turning-on of a discharge, in the case where the image forming apparatus is left standing for a predetermined period from the last image formation or every predetermined sheet number of the image formation. However, a manner in which the image forming apparatus is used varies.
An operation of the power switch (hard switch) is performed every day, and therefore the discharge current control is carried out every turning-on of the power switch every day. Further, in the case where the image form sheet number during a day (in a period from the turning-on of the power switch to a turning-off of the power switch), a period in which the image forming apparatus is left standing without being subjected to the image formation is long, so that the discharge current control is to be carried out every start of image formation after a lapse of a predetermined time from an end of last image formation. In the case where the image formation sheet number during the day as described above or the like case, a proportion of an energization time or a discharging time to the charging member in the discharge current control becomes large with respect to the energization time or the discharging time in the image forming operation. For that reason, the proportion largely influences a lifetime of the charging member in some cases. Particularly, in the case where the image forming apparatus is disposed in an environment such that equipment such as an air conditioner is provided and a temperature change is less, although the electric resistance fluctuation of the charging member is less and therefore necessity for effecting the discharge current control is relatively low, the discharge current control is carried out every turning-on of the power switch every day or every start of the image formation after the lapse of the predetermined time from the end of the last image formation, so that the charging member as the charger is deteriorated although a time in which the image forming operation is actually performed is small, and thus there was the case where the charging member or a process cartridge in which the charging member was incorporated had to be exchanged.